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[209.51.188.17]) by mx.google.com with ESMTPS id r4si917342ilo.48.2021.03.09.09.19.08 for (version=TLS1_2 cipher=ECDHE-ECDSA-CHACHA20-POLY1305 bits=256/256); Tue, 09 Mar 2021 09:19:08 -0800 (PST) Received-SPF: pass (google.com: domain of qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; Authentication-Results: mx.google.com; dkim=fail header.i=@redhat.com header.s=mimecast20190719 header.b=gYojolVD; spf=pass (google.com: domain of qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom="qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org"; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from localhost ([::1]:55464 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lJg0h-0000lp-Oo for alex.bennee@linaro.org; Tue, 09 Mar 2021 12:19:07 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:44912) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lJf5y-0006RW-TH for qemu-devel@nongnu.org; Tue, 09 Mar 2021 11:20:30 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:42602) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lJf5q-0002G3-CX for qemu-devel@nongnu.org; Tue, 09 Mar 2021 11:20:30 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615306821; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1jJJbOIxOY0Mxq+H2kcUM6uJwMCSAvdeDJz/Hci88oM=; b=gYojolVDbLntuoLfIPwjzCaBnihBZJsuh63w/dpfukK/ocMEe7Iov3MGbPTJDa2MzxF4vl SRTWjdCcFB8xAiK9kzvZgPnx0eJM7z0bBdep1oh2D+Dt0LC1ITT6klqRFimy6hK2skL39q cDVYizPDf9nhMYuxELvUC7Rd51gnFVI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-55-IJO7rgPAP8Cvint-yo1Ckw-1; Tue, 09 Mar 2021 11:20:19 -0500 X-MC-Unique: IJO7rgPAP8Cvint-yo1Ckw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5C96B80432E; Tue, 9 Mar 2021 16:20:17 +0000 (UTC) Received: from thuth.remote.csb (ovpn-112-72.ams2.redhat.com [10.36.112.72]) by smtp.corp.redhat.com (Postfix) with ESMTP id B62FB60C17; Tue, 9 Mar 2021 16:20:07 +0000 (UTC) To: "Dr. David Alan Gilbert" References: <20201217014941.22872-1-zhukeqian1@huawei.com> <20201217014941.22872-3-zhukeqian1@huawei.com> <65c92236-5212-f725-047a-cb1d231eff25@redhat.com> <759785ef-f29e-f05f-9f2f-357e71ae3680@huawei.com> <11854ebf-ed88-496d-8381-5385ef1b403a@redhat.com> From: Thomas Huth Subject: Re: [PATCH v2 2/2] accel: kvm: Add aligment assert for kvm_log_clear_one_slot Message-ID: <48fd9bee-4542-533a-b893-7acf3744fe36@redhat.com> Date: Tue, 9 Mar 2021 17:20:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.251, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Andrew Jones , jiangkunkun@huawei.com, qemu-devel@nongnu.org, Peter Xu , qemu-arm@nongnu.org, Gerd Hoffmann , wanghaibin.wang@huawei.com, Zenghui Yu , Paolo Bonzini , Keqian Zhu Errors-To: qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org Sender: "Qemu-devel" X-TUID: TogXET+FsFgT On 09/03/2021 15.57, Dr. David Alan Gilbert wrote: > * Thomas Huth (thuth@redhat.com) wrote: >> On 09/03/2021 15.05, Keqian Zhu wrote: >>> >>> >>> On 2021/3/9 21:48, Thomas Huth wrote: >>>> On 17/12/2020 02.49, Keqian Zhu wrote: >>>>> The parameters start and size are transfered from QEMU memory >>>>> emulation layer. It can promise that they are TARGET_PAGE_SIZE >>>>> aligned. However, KVM needs they are qemu_real_page_size aligned. >>>>> >>>>> Though no caller breaks this aligned requirement currently, we'd >>>>> better add an explicit assert to avoid future breaking. >>>>> >>>>> Signed-off-by: Keqian Zhu >>>>> --- >>>>> accel/kvm/kvm-all.c | 7 +++++++ >>>>> 1 file changed, 7 insertions(+) >>>>> >>>>> --- >>>>> v2 >>>>> - Address Andrew's commment (Use assert instead of return err). >>>>> >>>>> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c >>>>> index f6b16a8df8..73b195cc41 100644 >>>>> --- a/accel/kvm/kvm-all.c >>>>> +++ b/accel/kvm/kvm-all.c >>>>> @@ -692,6 +692,10 @@ out: >>>>> #define KVM_CLEAR_LOG_ALIGN (qemu_real_host_page_size << KVM_CLEAR_LOG_SHIFT) >>>>> #define KVM_CLEAR_LOG_MASK (-KVM_CLEAR_LOG_ALIGN) >>>>> +/* >>>>> + * As the granule of kvm dirty log is qemu_real_host_page_size, >>>>> + * @start and @size are expected and restricted to align to it. >>>>> + */ >>>>> static int kvm_log_clear_one_slot(KVMSlot *mem, int as_id, uint64_t start, >>>>> uint64_t size) >>>>> { >>>>> @@ -701,6 +705,9 @@ static int kvm_log_clear_one_slot(KVMSlot *mem, int as_id, uint64_t start, >>>>> unsigned long *bmap_clear = NULL, psize = qemu_real_host_page_size; >>>>> int ret; >>>>> + /* Make sure start and size are qemu_real_host_page_size aligned */ >>>>> + assert(QEMU_IS_ALIGNED(start | size, psize)); >>>> >>>> Sorry, but that was a bad idea: It triggers and kills my Centos 6 VM: >>>> >>>> $ qemu-system-x86_64 -accel kvm -hda ~/virt/images/centos6.qcow2 -m 1G >>>> qemu-system-x86_64: ../../devel/qemu/accel/kvm/kvm-all.c:690: kvm_log_clear_one_slot: Assertion `QEMU_IS_ALIGNED(start | size, psize)' failed. >>>> Aborted (core dumped) >>> Hi Thomas, >>> >>> I think this patch is ok, maybe it trigger a potential bug? >> >> Well, sure, there is either a bug somewhere else or in this new code. But it's certainly not normal that the assert() triggers, is it? >> >> FWIW, here's a backtrace: >> >> #0 0x00007ffff2c1584f in raise () at /lib64/libc.so.6 >> #1 0x00007ffff2bffc45 in abort () at /lib64/libc.so.6 >> #2 0x00007ffff2bffb19 in _nl_load_domain.cold.0 () at /lib64/libc.so.6 >> #3 0x00007ffff2c0de36 in .annobin_assert.c_end () at /lib64/libc.so.6 >> #4 0x0000555555ba25f3 in kvm_log_clear_one_slot >> (size=6910080, start=0, as_id=0, mem=0x555556e1ee00) >> at ../../devel/qemu/accel/kvm/kvm-all.c:691 >> #5 0x0000555555ba25f3 in kvm_physical_log_clear >> (section=0x7fffffffd0b0, section=0x7fffffffd0b0, kml=0x555556dbaac0) >> at ../../devel/qemu/accel/kvm/kvm-all.c:843 >> #6 0x0000555555ba25f3 in kvm_log_clear (listener=0x555556dbaac0, section=0x7fffffffd0b0) >> at ../../devel/qemu/accel/kvm/kvm-all.c:1253 >> #7 0x0000555555b023d8 in memory_region_clear_dirty_bitmap >> (mr=mr@entry=0x5555573394c0, start=start@entry=0, len=len@entry=6910080) >> at ../../devel/qemu/softmmu/memory.c:2132 >> #8 0x0000555555b313d9 in cpu_physical_memory_snapshot_and_clear_dirty >> (mr=mr@entry=0x5555573394c0, offset=offset@entry=0, length=length@entry=6910080, client=client@entry=0) at ../../devel/qemu/softmmu/physmem.c:1109 >> #9 0x0000555555b02483 in memory_region_snapshot_and_clear_dirty >> (mr=mr@entry=0x5555573394c0, addr=addr@entry=0, size=size@entry=6910080, client=client@entry=0) >> at ../../devel/qemu/softmmu/memory.c:2146 > > Could you please figure out which memory region this is? > WTH is that size? Is that really the problem that the size is just > crazy? The answer is one stack frame below... >> #10 0x0000555555babe99 in vga_draw_graphic (full_update=0, s=0x5555573394b0) >> at ../../devel/qemu/hw/display/vga.c:1661 The vga code basically does this: region_start = (s->start_addr * 4); region_end = region_start + (ram_addr_t)s->line_offset * height; region_end += width * depth / 8; /* scanline length */ region_end -= s->line_offset; ... memory_region_snapshot_and_clear_dirty(... region_end - region_start...); Thus it uses a size that is nowhere guaranteed to be a multiple of the page size. A similar usage can be seen in other devices, too (e.g. sm501.c), so either there is a bug in the assert() statement, or we have a problem with many devices... Thomas